1. Field of the Invention
This invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a semiconductor device having aluminum-base alloy lines.
2. Description of the Prior Art
FIGS. 5A through 5D show a prior art method of fabricating a semiconductor device. As shown in FIG. 5A, an oxide film 2 is formed on a silicon substrate 1 to cover circuit elements (not shown), for example MOSFETs, formed on the silicon substrate 1. Then, as shown in FIG. 5B, an aluminum-base alloy film 3 containing a few percent of silicon and copper is deposited on the oxide film 2. After the aluminum-base alloy film 3 is deposited on the oxide film 2, a thin, uneven native oxide film (passive film) 4 is grown on the surface of the aluminum-base alloy film 3. Thereafter, the silicon substrate 1 is cleaned with fuming nitric acid, rinsed with pure water, and then dried. After that, as shown in FIG. 5C, a resist 6 defining a line pattern (wiring pattern) formed on the aluminum-base alloy film 3 using a photolithography technique, and given portions of the aluminum-base alloy film 3 are selectively dry-etched using the resist 6 as an etch-mask, to form an aluminum-base alloy line (wiring) 3a. As shown in FIG. 5D, the resist 6 remaining on the aluminum-base alloy line 3a is removed by an ashing process using an oxygen-plasma, and organic residues on the aluminum-base alloy line 3a are removed by a cleaning process using fuming nitric acid.
In the prior art method, since the thin oxide film (passive film) 4 is unevenly grown on the deposited aluminum-base alloy film 3, pinholes (corrosion holes) are formed by corrosion, during the step of cleaning the substrate 1 with fuming nitric acid, in the aluminum-base alloy film 3 at positions indicated by arrows A in FIG. 5B and arrows B in FIG. 5D.
According to the study conducted by the inventor, et al., it has been found that the corrosion holes of the aluminum-base alloy film 3 and the aluminum-base alloy line 3a are formed not during the step of immersing or dipping the substrate 1 into the fuming nitric acid but during the subsequent step of rinsing with pure water. An aluminum-base alloy film and line containing at least one kind of alloying element (e.g., silicon, copper, silicon and copper, and so on) other than aluminum can easily be subjected to corrosion during the rinsing step due to the galvanic effects between the alloying element and aluminum, which eventually leads to a disconnection failure in the aluminum-base alloy line 3a.